I presume you mean federal level? A key term here.
Just enforcing whatever level of law for the department he's assigned to? Thus...requiring federal law? Probably backed at this stage by at least federal law, SCOTUS ruling, if not Constitutional amendment if states are found not willing to succumb to such a system?
Otherwise you just have fifty different systems. Which leaves us mostly where we are right now just only slightly more organized. Just with people whining about New York State instead of NYPD or California instead of LAPD.